This invention relates generally to the field of spark plug gaskets, and more particularly to an improved means and method for installing a captive type which remains in engaged condition upon the threaded shank of a spark plug during installation and removal. The art is presently at a very highly developed state, and the invention lies in specific constructional details which permits simplification of the fabrication of the gasket, and the impartation of a completed configuration of the locking flange portion thereof at the time of installation.
In my recently issued U.S. Pat. No. 4,003,120; dated Jan. 8, 1977, entitled Captive Type Spark Plug Gasket And Tool For Installing Same, there is disclosed a captive type gasket of the class described including a plurality of interconnected compressible flanges which accomplish a sealing function between the plug body and the cylinder head, and an inwardly extending generally angularly disposed flange which is staked into position to engage the undercut portion of the threaded shank of the plug body. The free edge of the last mentioned flange is folded upon the free edge thereof to provide an effective thickness approximating the medial thickness of the spiral groove on the threaded portion of the shank to resist the tendency of the gasket to cross-thread when the plug is removed from the cylinder head, and thereby remain attached to the plug. In one embodiment, the free edge is folded through 180.degree.. In another embodiment, the free edge is folded through approximately 90.degree. relative to the plane of the remaining portion of the inwardly turned flange to provide the equivalent result.
While these constructions are effective for the contemplated purpose, the fabrication of the gasket requires the formation of the fold upon the free edge of a locking flange in either case. The formation of the fold requires an additional one or more progressive die stations, and the necessity of maintaining very close tolerances in the dies located at these stations.
The patent also discloses means for the installation of the above described gaskets. However, although the means performs both the function of aligning the gasket on the plug body, and subsequently folding the locking flange to maintain it in place, the means does require the use of gaskets including the disclosed fold edges, in order to obtain the contemplated result.